Disc brakes have been commonplace in automobiles for decades. Most modern cars have disc brakes on the front wheels, and often on all four wheels. Disc brakes generally include a rotor or disc connected to the wheel and/or axle, and a pair of brake pads on either side of the rotor that are squeezed inwardly against the rotor by means of a caliper. The caliper may be actuated, for example, hydraulically or pneumatically.
Brake pads generally consist of a metal backing plate with friction material on one side to contact the rotor. The brake pads move inward in relation to the rotor when the brakes are actuated and return in an outward direction thereafter. The caliper typically includes hardware or clips that are mounted in the caliper at the ends of the brake pads to position the brake pads in the caliper. While the hardware generally retains the position of the brake pads in some respects, it often does not ensure the brake pads return to and remain in their outward position after brake actuation.
It is common in disc brakes to have a return spring mounted between the two brake pads to assist with returning the brake pads to a rest position after braking. Typically, a single spring is mounted in the middle of the two brake pads and engages the upper parts of the backing plates. See, for example, U.S. Pat. No. 7,467,693 to Barbosa et al. The return spring helps to prevent the pads from dragging on the rotors when braking is not desired. However, such a spring may provide an uneven return and retention force on the brake pads. Thus, in some instances, the brake pads may become misaligned with respect to rotor and portions of the brake pads could drag on the rotor despite the presence of the spring. Further, the spring generally requires that holes in each of the backing plates to receive the spring. Drilling of these holes adds cost and delay to manufacturing.
Some attempts have been made to position return mechanisms at the axial ends of brake pads. U.S. Pat. No. 8,869,950 to Maehara et al. describes a disc brake with pad clips and return springs. Maehara uses a return spring which is attached to a pad clip. This design requires a series of constraining sections and protruding pieces on the pad clip to retain the spring. It also requires two separate pieces which complicates manufacturing and reduces reliability in that the parts can separate.
U.S. Pat. No. 8,397,880 to Chelaidite discloses a pad retraction device. As shown in FIG. 6, some embodiments employ a separate spring as in Maehara. As recognized in Chelaidite, adding a spring can adversely affect the vibration and/or noise performance of the braking system. The remaining embodiments use arms with an overlapping portion or lip on the end of the arm to pull the brake pads outward. This design is complex to manufacture requiring several bends and may lack rigidity due to the overlapping portion and may wear over time. A similar design is disclosed in U.S. Patent Application Publication No. 2010/0051393 to Arioka.
Such attempts at providing return mechanisms do not provide a viable solution to overcome the drawbacks of the customary central return spring.